1. Technical Field
The present disclosure relates to a power supply apparatus. More specifically, the present disclosure relates to a power supply apparatus capable of supplying power for a programmable logic controller (PLC), especially power for PLC memory backup and RTC operation even in an event of power-off by way of utilizing advantages of a battery module and a super capacitor module.
2. Description of the Related Art
In a programmable logic controller (PLC), a variety of devices such as ferroelectrics RAM (FRAM), a flash memory, etc., are used for data backup such as user programs or documents, etc. Such devices have to be able to store data even after their functional modules are tuned off. Among others, a FRAM has advantages in that it has fast data write time and does not require additional battery backup. However, its cost increases with memory capacity and there is a limit on data storage capacity. A flash memory, on the other hand, has larger data storage capacity and is less expensive, but it takes longer data write time. Because of such issues of data storage capacity and data write time, a fast SRAM device is frequently used since it is cheap. A SRAM requires a battery and a circuit for backup to keep supplying power. A SRAM and the like receive power from an internal or external power supply. Power supplies may be household or industrial power supplies (e.g., 110 V service, 220 V service, etc.), or may be an internal adaptor or charging device. Non-volatile memories such as a SRAM may be critically damaged, e.g., data loss if a power supply is suddenly turned off. In order to prevent this, manufactures have developed a variety of backup power supplies to cope with sudden power-off of power supplies.
Even in a PLC system, functional modules including a central processing unit (CPU) module that require data backup include their own batteries and circuits for backup. Such a battery and a circuit for backup included in each of the functional modules monitor the level of signals from the main power source. If the level of signals is out of a normal range, power is supplied to a variety of backup devices that need to be supplied with power such as an SRAM or real-time clock (RTC), thereby preserving data.
As shown in FIG. 1, for a typical backup power supply apparatus using a battery, a battery has limited lifetime, and the battery is rapidly discharged after a particular lifetime. Accordingly, batteries have to be replaced periodically due to limited lifetime, and thus maintenance cost incurs for replacing batteries.